Vehicles may use various types of combustion modes in combination with a hybrid powertrain to achieve improved vehicle efficiency.
One example is described in U.S. publication 20050173169, which uses a homogeneous charge compression ignition combustion (HCCI) engine as one form of the auto-ignition operation. In this system, power production from the HCCI engine in operation may be decoupled from, or assist in, responding to driver power demand. When a driver power demand is greater than what can be provided by the HCCI engine, the addition of power from the powertrain's reversible secondary power source (e.g. one or more reversible electric motor/generator(s) or reversible hydraulic pump/motor(s)) is used. Likewise, when a driver power demand is less than a value produced by the engine, a portion of power is converted into storable energy for storage in an energy storage device.
The inventors herein have recognized a disadvantage with such an approach. In particular, while driver demand may be one influence on engine operation and use of a supplemental power source to supply or store energy, various transient conditions may occur even when a driver demanded response is changing slowly or not at all. For example, during a transmission gear change, required engine output may vary dramatically and may increase and/or decrease below a value that can be provided via an engine operating with at least one cylinder carrying out compression ignition.
As such, in one example, a method for controlling an engine and a supplemental torque apparatus of a vehicle, the vehicle having a transmission coupled to the engine, may be used. The method comprises operating at least one cylinder with at least partial auto-ignition combustion; and during a transient gear change where the engine temporarily encounters a low load and low speed operating condition, increasing loading on the engine via the supplemental torque apparatus so that the at least one cylinder may remain operating with at least partial auto-ignition combustion.
In this way, it is possible to compensate for conditions other than the requested drive torque that may affect the appropriate selection of supplemental torque and engine torque in an engine carrying out auto-ignition operation. For example, during a transmission gear change which may otherwise cause the engine to operate in a low speed and/or low load condition beyond that in which auto-ignition operation is feasible, the engine may avoid or reduce transitions in the combustion mode by utilizing the supplemental torque apparatus to increase the effective engine load without adversely affecting the vehicle drive torque that the driver has requested.
Note that various terms for auto-ignition may be used, such as homogenous charge compression ignition, or controlled auto-ignition, or partial HCCI operation, etc. Note also that the low speed and low load thresholds may be a function of various operating conditions and engine/vehicle design parameters.